You will need the speed dial extension unfortunately, where you can create or edit the google link according to your desires. This Opera now is quite unfriendly directly. It intends to hide off the tweaking options whereas in the previous versions, users could have that freedom.
To install the extension you will first need to go to : Menu > Extensions > Get extensions. Then do the search for Speed Dial in the "search for add-ons" box. There may be a few various kinds in the result. I think the FVD Speed Dial is still the easiest and best.